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Derive Keplers 3rd law

Equate gravitational force (GMm/r^2) to centripetal force (mv^2/r). Rearrange to get v^2=GM/r. Due to the approximated circular orbit v=2pir/T so v^2=4pi^2r^2/T^2. Therefore GM/r=4pi^2r^2/T^2. Rearrangin...

Answered by Michael S. • Physics tutor

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A projectile is fired at an angle of 30 degrees from the horizontal, it reaches a maximum height of 12m above the ground before coming to rest 600m from its initial starting point at the same level. What is the initial speed of the projectile?

At first glance this question seems require solving in several steps, splitting horizontal and vertical components, taking a value for time from the motion under constant acceleration and then applying th...

Answered by Joseph S. • Physics tutor

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A geostationary satellite is orbiting Earth, a) What is meant by a geostationary orbit? b) Calculate the height at which the satellite orbits above the surface of the Earth. The radius of the Earth is 6400km and its mass is 6x10^24 kg.

a) A geostationary orbit is when the satellite remains vertically above the same point on the equator at all all times and consequently has an orbital period of 24 hours. b) Use the equation T^2=4(PI)^2(r...

Answered by Edward N. • Physics tutor

19587 Views

A DVD is dropped from rest. The DVD does not reach terminal velocity before it hits the ground. Explain how the acceleration of the DVD varies from the instant it is dropped until just before it hits the ground.

In the instant when the DVD is dropped, it will have an acceleration of g, with no drag force acting on it as it is not moving. As the DVD accelerates downwards, the drag force acting on it increases and ...

Answered by Dylan H. • Physics tutor

3675 Views

A kettle is found to output 65J when its input energy is 100J. What is the efficiency of the kettle, and what happens to the rest of the energy?

Efficiency=useful energy /input energy x 100, so for the kettle, efficiency = 65/100 x 100 = 65% efficient. The rest of the energy is wasted as heat energy in the kettle/sound energy.

Answered by Joshua L. • Physics tutor

20080 Views